1. Field of the Invention
The present invention relates to a golf club, and, more particularly, the present invention relates to a golf club with a coefficient of restitution adjustment device.
2. Description of the Related Art
Golf club heads come in many different forms and makes, such as wood- or metal-type, iron-type (including wedge-type club heads), utility- or specialty-type, and putter-type. Each of these styles has a prescribed function and make-up. The present invention relates to hollow golf club heads, such as wood-type and utility-type (generally referred to herein as wood-type golf clubs).
Wood-type type golf club heads generally include a front or striking face, a crown, a sole, and an arcuate skirt including a heel, a toe, and a back. The crown and skirt are sometimes referred to as a “shell.” The front face interfaces with and strikes the golf ball. A plurality of grooves, sometimes referred to as “score lines,” may be provided on the face to assist in imparting spin to the ball. The crown is generally configured to have a particular look to the golfer and to provide structural rigidity for the striking face. The sole of the golf club contacts and interacts with the ground during the swing.
The design and manufacture of wood-type golf clubs requires careful attention to club head construction. Among the many factors that must be considered are material selection, material treatment, structural integrity, and overall geometrical design. Exemplary geometrical design considerations include loft, lie, face angle, horizontal face bulge, vertical face roll, face size, sole curvature, center of gravity, and overall head weight. The interior design of the club head may be tailored to achieve particular characteristics, such as by including hosel or shaft attachment means, perimeter weighting on the face or body of the club head, and fillers within hollow club heads. Club heads typically are formed from stainless steel, aluminum, or titanium, and are cast, stamped as by forming sheet metal with pressure, forged, or formed by a combination of any two or more of these processes. The club heads may be formed from multiple pieces that are welded or otherwise joined together to form a hollow head, as is often the case of club heads designed with inserts, such as sole plates or crown plates. The multi-piece constructions facilitate access to the cavity formed within the club head, thereby permitting the attachment of various other components to the head such as internal weights and the club shaft. The cavity may remain empty, or may be partially or completely filled, such as with foam. An adhesive may be injected into the club head to provide the correct swing weight and to collect and retain any debris that may be in the club head. In addition, due to difficulties in manufacturing one-piece club heads to high dimensional tolerances, the use of multi-piece constructions allows the manufacture of a club head to a tight set of standards.
The distance a golf ball travels after impact with a golf club is dictated by the magnitude and direction of the ball's translational and rotational velocities. Golf ball travel distance is a function of the total kinetic energy imparted to the ball during impact with the club head, neglecting environmental effects. During impact, kinetic energy is transferred from the club and stored as elastic strain energy in the club head and the ball. After impact, the stored elastic energy is transformed back into kinetic energy in the form of translational and rotational velocity of the ball as well as of the club. Since the collision is not perfectly elastic, a portion of the energy is dissipated as heat, club head vibration, and viscoelastic relaxation of the ball. Golf ball landing accuracy also is driven by a number of factors. Some of these can be attributed to club head design. Of primary concern are center of gravity and club face flexibility.
Recently, in an effort to increase the golf ball travel distance, especially among amateur golfers, wood-type golf clubs with large head sizes have been introduced. The increased head size allows the club to possess a higher moment of inertia (MOI), which translates to a greater ability to resist club twisting resulting from off-center hits. Inertia is a property of matter by which a body remains at rest or in uniform motion unless acted upon by some external force. MOI is a measure of the resistance of a body to angular acceleration about a given axis, and is equal to the sum of the products of each element of mass in the body and the square of the element's distance from the axis. Thus, as the distance from the axis increases, the MOI increases. As the MOI increases, the stability, playability, and forgiveness of the club head increases.
The weights of these large club heads typically have been kept within acceptable limits by using lighter materials and thinner shell thicknesses. The club head faces also have been becoming steadily thinner. Thinner faces maximize the Coefficient of Restitution (COR), which means that the face will rebound more upon impact and impart more energy to the ball, thereby increasing shot length. A corollary to COR is contact time (CT), which is a measurement of the duration of the contact between the club face and the ball. CT increases and decreases as COR increases and decreases. The COR and CT of typical golf club heads are results of the club head design, particularly face thickness, and are not adjustable.
The United States Golf Association (USGA) and the Royal and Ancient Golf Club of St. Andrews (R&A), the governing bodies of golf, have instituted limitations upon the COR of golf clubs. It is important that club heads not exceed these limitations. Customized COR's may also be desired. For example, a particular player (such as a Tour player) may desire a specific COR under the USGA and R&A limits. Thus, what is needed is a golf club head with an adjustable COR.